The present invention relates to electric machines, and more particularly to electric machines with segmented stators.
Electric machines such as motors and generators include a rotor that is a rotating member of the electric machine and a stator that is a stationary member of the electric machine. In some applications, the rotor is rotatably mounted inside of the stationary stator. An air gap is defined between a radially outer surface of the rotating rotor and a radially inner surface of the stationary stator. When debris falls into the air gap, a locked rotor condition may occur.
Manufacturers sometimes integrate the electric machines into larger systems. Debris may enter the air gap during assembly of the electric machine and/or during use in the field. Some manufacturers specify strict cleanliness standards during the assembly process. In addition, manufacturers also require sealed stator and rotor packages that prevent the locked rotor condition.
There are several conventional methods for preventing debris from entering the airgap during assembly and subsequent use in the field. During the assembly process, the electric machine manufacturer strictly enforces cleanliness specifications and performs visual inspections of the electric machines after assembly. A stator varnish and bake system may also be employed. Plastic encapsulation and resin potting have also been employed.
All of the conventional methods generally increase the time that is required to manufacture the electric machine, which increases the cost of the electric machine. In addition, the final three conventional methods described above typically require a significant amount of capital investment. The conventional solutions become less economical when the electric machine includes a segmented stator. The handling of each of the stator segments during varnish, plastic encapsulation or resin potting increase processing expense. In some applications, only one end of the stator is open, which makes it difficult or impossible to generate enough pressure to overmold or resin pot the entire stator or to ensure that enough varnish covers the closed end of the motor.
An electric machine according to the present invention includes a stator with a plurality of circumferentially-spaced stator segment assemblies. Each stator segment assembly includes a stator segment core, an endcap that is attached to the stator segment core, and winding wire that is wound around the endcap and the stator segment core. The endcap provides first and second axial mating surfaces. A rotor rotates relative to the stator and defines an airgap between an outer diameter of the rotor and the inner diameter of the stator. The first axial mating surface of one stator segment assembly mates with the second axial mating surface of an adjacent stator segment assembly to provide axial seals that prevent entry of debris into the airgap.
In other features of the invention, the endcaps provide first and second circumferential end surfaces on axially opposite ends of the stator segment assemblies. First and second annular seals bias the first and second circumferential end surfaces to provide circumferential seals at axially opposite ends of the stator. The annular seals, the axial seals and the circumferential seals cooperate to prevent the entry of debris into the airgap.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.